(i) Field of the Invention
This invention relates to means for spooling and/or storing faired cable aboard ship.
(ii) Description of the Prior Art
Underwater SONAR (abbreviated from "Sound Navigation and Ranging") is finding ever-increasing use in the fields of navigation, mapping, depth finding, fish finding, and detection of wrecks and enemy vessels. SONARS as used by surface vessels may be classified either as (1) hull mounted systems, wherein an underwater sound transducer or array is mounted on the hull of the vessel; or (2) variable depth systems, wherein an underwater sound transducer or array is mounted in a body towed from the vessel.
To be truly useful, a variable depth system must be capable of placing the towed vehicle with its enclosed array well below the thermocline layers in the ocean. This may mean towing with several thousand feet of cable. To obtain maximum depth with a given length of cable, cable drag is reduced by enveloping the entire length of cable with streamlined fairings. These fairings are segmented into short lengths with interconnecting links to allow bending or wrapping of the cable without fracturing the fairings.
A problem arises, however, in the spooling or storing of such a faired cable aboard ship. The tailpieces of the segmented fairings are almost always made of lightweight plastic, and it is not possible to spool the cable in multiple layers onto a drum without crushing the fairings in all but the top layer. This means that, in usual practice, only single-layer winding could be used with a segmented fairing cable. If the cable is very long, the winding drum may be huge. This would cause topside weight and space problems, fleet angle problems and might necessitate the use of extra power.
A number of methods of circumventing these problems have been proposed in the past. For example, U.S. Pat. Nos. 2,397,957 issued Apr. 9, 1946 to H. B. Freeman; 2,401,783 issued June 11, 1946 to K. H. Wilcoxon; 3,209,718 issued Oct. 5, 1965 to R. L. Rather et al; and 3,241,513 issued Mar. 22, 1966 to R. L. Rather et al, all attempt to solve the problem by the use of removable fairings. With such fairings, the base cable can be spooled as a multi-layer onto a storage drum. However, a major disadvantage is that time is consumed stripping the fairings on cable recovery and installing the fairings during cable payout. This could be particularly difficult in high sea states. A problem also arises in storing the removed fairings without damage.
Canadian Pat. No. 902,577 issued June 13, 1972 to N. E. Hale proposed to solve the problem by using multiple concentric drums. However, there are many disadvantages inherent in a drum of this construction. Firstly, the outer drums must be slotted across the face of the shell and this may severely weaken the drums. Secondly, the cable or fairings or both may be severely damaged at the points of inflection in bridging the shell gaps. Thirdly, in one embodiment, one drum is connected to the other by short-stroke hydraulic cylinders connected up to a manifold system with quick-release connections. Frequent use of this method aboard ship will result in hydraulic spills, and contamination being introduced into the hydraulic system. In another embodiment, the outer drum is given motive power by wedging up the tailpieces of the fairings into contact with the roof of an access chamber in the outer drum. This may damage and crush the fairings.
It has also been suggested to use two concentric drums with unbroken shell faces which screw into one another. The major disadvantage of such proposal was that with all the cable paid out, the drums must be completely unscrewed, and in this condition they take up as much space and weight as the one single layer drum previously referred to and with a great increase in complexity.
Another proposal is shown in Canadian Pat. No. 671,172 issued Sept. 24, 1963 to Nantec Corporation which provided a level winding device disposed at right angles to a cable storage drum. A key feature of this invention was the use of pressure rollers to exert a squeezing force on the cable. It is virtually impossible to exert such a force on cable enclosed with segmental fairings for the purpose of gaining traction. In addition, such squeezing force might damage the fairings, which are somewhat fragile.
Yet another proposal was shown in Canadian Pat. No. 671,172 issued June 18, 1974 to American Chain and Cable Co. Inc. which provided a cable trained over a double capstan, with its other end extending through a guide into a cylindrical container disposed at right angles to the capstan. Key features of this proposal were the use of separate traction and storage drums. The storage drum and its drive alone would take up as much space as a single simple powered drum used for both power and storage. In other words, and aside from other drawbacks, as a means of spooling extra long lengths of segmentally faired cable (all in one single layer), the traction winch with separate storage drum is the most space-consuming solution of all, and there would be no room for it aboard most naval vessels.